Mbox 2 mini play distorted sound

I use Pro Tools 11 and Mbox 2 mini
It's running on New Mac Book Pro i7 and OS 10.9.5

Problem
Audio playback normal change to distorted sound
Back to normal once you disable and enable playback engine 'Mbox 2 mini" again, but It will distorted again after couples minutes
Beside Pro Tools operation, I used Mbox2 mini as output interface for playback song from ITUNE also had same problem
I wonder it's not enough buffer for USB-audio playback?

Trouble Shooting
I tried following already
- updated Pro Tools 11 version
- set H/W buffer to max 1024
- install latest Mbox 2 mini driver
- turn off bluetooth and WiFi connection
- Directly plug into Mac Book Pro USB port

Anyone can help..? Please!!!!:confused: